The present invention relates to a dental handpiece which has at least two drive shaft sections, which are arranged with their axes forming an angle with one another and form part of a drive train for transmission of the rotary motion from a drive motor of the handpiece to an acceptance socket which receives a tool and is rotatably mounted in a head part of the handpiece. To transfer motion between the drive section, the drive sections are provided with gears and at least one of the drive sections is provided with two coaxial gears having different numbers of teeth so that by axially shifting one of the sections relative to the other section, different gear combinations are in meshing engagement to produce different drive ratios between the two sections.
In a known dental handpiece such as disclosed in German A.S. No. 1,219,170, the drive train means, which transfers rotation from the drive motor to the acceptance socket in the head part, is subdivided into two drive shaft sections with one of the drive shaft sections being in a handpiece part directly connected to the motor and the other drive shaft section being in a portion of the head part. One of the two drive shaft sections is provided with a single gear and the other is provided with a pair of coaxial gears arranged with their teeth lying essentially in one plane and having different numbers of teeth. By connecting the head part and the handpiece part together in different positions so that the shaft section having the single gear is in one of two axial positions, the single gear can be in meshing engagement with either the smaller or the larger gear on the other drive shaft section. By selecting the gears, it is possible to have a direct drive with a 1:1 ratio or either a step-up in the RPM's of 1:3 RPM ratio or a step-down with a 3:1 RPM ratio. To obtain this step-down ratio the pair of gears are connected to the end of the shaft section, which is supported in the head part and to obtain the step-up in the ratio, the pair of gears are provided on the shaft section supported in the handpiece part. While this dental handpiece enables providing two different drive ratios, in order to obtain both a step-up and step-down of the ratios, various drive motors and/or handpiece and head parts for connection to the drive motors, which parts have been appropriately designed, must be provided. Since a Dentist will work with both a step-down as well as step-up drive RPM's, he must have a plurality of drive motors, or respectively, handpiece parts of the drive side according to this known handpiece structure.
A further disadvantage of the above mentioned dental handpiece is that the gear arrangement or transmission, which provides the two step ratio, greatly increases the exterior diameter of the handpiece particularly in the area of the bend of the angle piece. Furthermore, because the change in the RPM is obtained by connecting the handpiece portion and the head part together in different positions relative to the axis, the handpiece cannot have a portion that is free to rotate or twist relative to the drive motor. Moreover, the angle at the angle piece for this design is approximately 20.degree. to the longitudinal axis of the drive motor and such an angle, which is necessary for this structure is to abrupt and thus reduces the ease in the manipulation of the handpiece. Due to the large overall diameter, the abrupt angle at the angle piece and the lack of a rotatable connection, manipulation of this handpiece structure leaves something to be desired.